BACKGROUND: Corona Virus Disease 2019 (COVID-19) has caused great changes in daily activities, especially in children. In Spain, to avoid infections, a home quarantine was declared, which caused a drastic reduction in daily or weekly physical activity in children. OBJECTIVE: to analyse the balance performance after the COVID-19-induced quarantine on children's balance, through the use of balance tests, considering the type of sport practiced. METHODS: an observational and longitudinal study was carried out with a sample size of 150 healthy children (69 boys and 81 girls) with a mean age of 10.02 ± 1.15 years. Postural control was evaluated under different equilibrium conditions before and after the quarantine period. Two data collections using the Gyko system were compared, with a difference of 8 months between them. In addition, the influence of foot type and physical activity was analysed. RESULTS: After the quarantine, statistically significant differences were found in terms of balance results, which were worse than before (p < 0.05). Postural control was not influenced by the type of sport practiced (i.e., individual, collective and / or not practicing sport), nor by the surface which the test was performed (p > 0.05). Physically active children (i.e., individual and / or collective sport) presented worse results than physically inactive children. A statistically significant impairment in terms of balance was demonstrated in children who performed high and moderate physical activity (p < 0.05). CONCLUSIONS: After the quarantine period, a significant reduction in balance performance was found in children. The findings suggest that regular physical activity benefits postural control. Loss of balance does not differ in postural stability by the type of sport practised. Postural stability is not influenced by the type of footprint after the period of physical inactivity. Postural control is influenced in children with a great level of physical activity.